Build a Foxhole

This article explains how to build a standard US Army defensive fighting position.

Steps

Select an appropriate site.
Dig a rectangular hole 6.5' by 3'. The hole should be deep such that if you stand in the hole, the walls come up to your armpits.
Dig sumps four or five inches wide stretching the entire width of the hole on the left and right sides. Make these at least two feet deep. These are there so you can dispose of any grenades that are thrown into your foxhole.
About a foot and a half in front of the hole, place a row of sandbags two bags high and 6.5' long. Similarly, place rows of sandbags to the left and right sides of the hole. These support the roof and provide protection from shrapnel and bullets.
In the rear, place a centered row of sandbags two sandbags high 1.5' away from the hole but only 3.25' long.
Place 4"-6" logs across the top stretching from the back wall of sandbags to the front, cover with a tarpaulin or a poncho for waterproofing, then cover with a small layer of soil. This provides for shelter from the elements and fragmentation.
Camouflage the entire thing and be sure to hide or disguise the displaced soil.

4"-6" diameter logs can be used in the place of sandbags if your wife won't let you borrow her pillowcases.
Don't use explosives. They can be dangerous and sometimes even illegal. Don't make the mistake I did.
Roots are awful to dig through. Bring a hatchet, pruning shears, or better still, choose a site that isn't near any trees.